There should be nothing wrong with the script. This is a server issue I have seen twice in 2 years
It does not like the adm-userg.php file called with the ppaction statement.
Try downloading these two admin files and seeing if these work as this is what I did for a photopost customer a ways back to get it working
One of those strange things you will never know why it happens as its weird as every other script is called by a ppaction statement and works fine.